Enhancing the selectivity of Pd/C catalysts for the direct synthesis of H 2 O 2 by HNO 3 pretreatment

Pd/C catalysts are one of the most efficient catalysts for direct synthesis of H 2 O 2 from H 2 and O 2 (DSH), while pretreating the activated carbon by HNO 3 will influence the performance of the Pd/C catalyst. In this paper, a series of HNO 3 -pretreated and N 2 -calcinated activated carbon-supported Pd catalysts were prepared and evaluated for the DSH reaction at ambient temperature. The experimental results showed that using HNO 3 -pretreated activated carbon as the support enhanced H 2 O 2 selectivity greatly, and the highest H 2 O 2 selectivity of 90% was obtained on 20 wt% HNO 3 -pretreated catalyst. The catalysts were systematically characterized by multiple techniques including transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), N 2 adsorption–desorption, Boehm titration and other techniques. It was found that the textural properties of activated carbon did not affect the catalytic performance, while the effects of acid functional groups of activated carbon were supposed to improve the H 2 O 2 selectivity, and lower H 2 O 2 decomposition and hydrogenation capacities of the catalyst.